Electromagnetic shielding is provided at joints between removable panels of housings for electronic equipment and testing facilities to impede transmission of electromagnetic fields. Optimally, electromagnetic activity from external devices is prevented from effecting the shielded device while electromagnetic activity generated by the shielded device itself is also prevented from escaping the shielded enclosure. Electromagnetic shielding is often required for shielded enclosures such as, for example, doors of electronic laboratory rooms, casings of radio transmitters, receivers and computers and other similar facilities and equipment.
Commonly, such structures and equipment require shielding along gaps between surfaces of doors, access panels, drawers, cabinets or the like, where surfaces are repeatedly, or only possibly, moved relative to one another. For example, electrical components may be arranged individually in cases which are slid into and out of cabinets every time there arises a need to test, service or update the component. Accordingly, it is highly desirable for the casing to have electromagnetic shielding that is adapted to withstand the bi-directional shearing action induced upon it by each insertion and a removal of the casing into and from the cabinet. Similarly, electrical components may be arranged in a compartment accessible only through a pivoting door which must be opened and closed each time there arises a need to test, service or update the component. As with the casings, it is highly desirable for the mating surfaces of the door to have electromagnetic shielding that is adapted to withstand the "wiping" action induced thereon during each pivot of the door. Failing such characteristics, the electromagnetic shielding of the electrical component may become broken and the component along with the entire electrical system to which it is connected become vulnerable to or an emitter of electromagnetic interference.
Track mounted electromagnetic shielding devices such as that disclosed in U.S. Pat. No. 4,623,752 issued to Steen et al. have been previously proposed to provide acceptable electromagnetic shielding. However, track-mounted devices are not readily mountable or removable for repair or replacement since at least one part of such devices, namely the track, is separately secured to the surface by separate fasteners. Furthermore, the fastener receiving holes disposed in the track may also compromise the overall shielding effectiveness of the shielding device. For example, the carrier strip used in the Steen et al. device is mounted to a surface by separate push-in rivets and before the Steen et al. device can be fully mounted and assembled, the carrier strip must first be secured to the surface by the push-in rivets. Similarly, if the device needs to be replaced or repaired, the rivets must first be removed before the carrier strip can be removed. The extra step of having to insert or remove the rivet before the shielding device may be mounted or removed is an inconvenient step of the mounting or removal procedure. Moreover, the presence of holes for receiving the rivets is likely to reduce the overall shielding effectiveness of the Steen et al. device.
To avoid such inconveniences associated with track mounted devices while still providing acceptable electromagnetic shielding, it has been proposed to secure a shielding strip to a surface with a retaining clip. For example, in U.S. Pat. No. 4,760,214 granted to Bienia et al., an electromagnetic shielding device is disclosed having a clamping element that secures a shielding strip to a surface. The clamping element does not require a separate fastener in order to secure the clip to the mounting surface and, consequently, the shielding device may be readily mounted or removed without extensive assembly or disassembly steps.
Notable of clip mounted devices such as that disclosed in the Bienia et al. reference, however, is that the clamping element and the shielding element are only secured to each other when mounted on a surface. Consequently, when removed from the surface or prior to mounting on the surface, the clamping element and the shielding element become separated and thus each element is susceptible to becoming lost. Moreover, during the mounting procedure, care must be taken to ensure that the clamping element is situated correctly with respect to the shielding element and vice versa. Such added care causes the mounting procedure to become rather tedious.
Clip mounted devices such as that disclosed in the Bienia et al. patent may also experience undesirable stresses within the shielding element. Depending on how the shielding element is secured within the clamping element, concentrated stresses may be cyclically induced at certain locations on the shielding element. Such undesirable stresses may result in catastrophic failure of the shielding strip that would disrupt the integrity of the electromagnetic seal around the shielded item.